Labels are powerful things. Several years ago the anxiety and depression I've lived with all my adult life peaked, so I went to see my GP. "I feel really anxious and on edge," I told him. He handed me a questionnaire. I filled it in: Yes, I drink too much; No, I haven't tried to kill myself recently. "You're anxious," he told me, "take some of these beta-blockers. They'll help with your anxiety."

Counselling wasn't available, but I didn't care - being able to pop a few pills seemed a lot more convenient than opening up my wounds for some stranger to inspect.

Six months later I was even more anxious and depressed. The anti-anxiety pills hadn't had much effect, or at least if they had it was swamped by the hundred-plus units of alcohol I guzzled each week. I decided to go back to the doctor, but I wanted a different outcome this time, and so I came up with a cunning plan.

"I feel really… depressed," I told him. He handed me a questionnaire. I filled it in like before: Yes, I drink too much; No, I haven't tried to kill myself recently. "You're depressed," he told me, "take some of these anti-depressants. They'll help with your depression."

Labels are powerful things. They're also the subject of Jon Ronson's new book, The Psychopath Test, which I finished reading on the toilet last night.

The titular test is the Hare Psychopathy Checklist, a diagnostic tool developed by psychologist Robert Hare to detect psychopaths. Ronson is fascinated by the idea that psychopaths' personality traits might make them unusually effective at infiltrating the upper echelons of society, that entire wars and financial disasters could be traced back to one person's misfiring amygdala.

Armed with Hare's test he sets off to meet with an array of people who may or may not be psychopaths… and things rapidly become A Bit More Complicated Than That. If (like me) you're a fan of Ronson's meandering, gonzo style - far, far sharper than it seems at first glance - then you'll love it. On the other hand, if Louis Theroux documentaries make you want to throw things at the telly, it might grate a little.

The 'psychopaths running society' thesis is tackled only half-heartedly by Ronson, and he doesn't sound terribly convinced by it, at one point comparing the idea to a conspiracy theory. Much more interesting is the path he travels; from his initial delight in having the ability to detect psychopaths, to his later realization that in the wrong hands - in his hands - a diagnostic tool could easily become a weapon.

The label 'psychopath', Ronson discovers, is as easy to apply as it is difficult to remove, and the effects can be profoundly life-altering. No more so than in the chilling case of 'Tony', an inmate who claimed to have faked insanity to con his way into Broadmoor, and then found himself unable to get out. The book poses many more questions than it tries to answer.

If there's a criticism to be levelled at The Psychopath Test it's that the sheer breadth of areas covered leaves it feeling a little unsatisfying. The end came unexpectedly quickly, and I was forced to leave my porcelain sanctuary about a hundred pages earlier than I hoped to. I wanted more Ronson, even if it meant, as my Nan used to warn, getting piles.

An array of topics are touched on but left largely untapped, several of them worthy of substantial books in their own right. Ronson speaks to conspiracy theorists, criminals, and business experts, but the world of politics is largely untouched. A fascinating but all-too-brief section looks at the experiences of a researcher working in reality TV, a parasitic industry devoted to the exploitation of personality disorders for entertainment. Then there's the exploitation of labels by a pharmaceutical industry seeking to medicalise as much 'abnormal' behaviour as possible, a recurring theme that could bear much more attention.

But perhaps expanding on these would have muddied the message of the book. In documenting the struggles and uncertainties that come with trying to apply Hare's checklist responsibly and consistently, The Psychopath Test is a compelling reminder that labels are powerful, and that their power can be used for good or bad.

To this day I've not had a credible diagnosis for my pet torturer, so I've learned how to live with it, to accept it as a part of me. Perhaps there's a handy pill out there for me; but drugs are priced in labels. At times labels can seem convenient or comforting to hold on to, but get too attached and you may find that you're no longer holding the label - the label is holding you. And it might not even be the right one.